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/**
@page LPTIM_PWM_LSE LPTIM PWM Low Power example with LSE clock source
@verbatim
******************************************************************************
* @file LPTIM/LPTIM_PWM_LSE/readme.txt
* @author MCD Application Team
* @brief Description of the LPTIM PWM LSE example
******************************************************************************
*
* Copyright (c) 2019-2021 STMicroelectronics.
* All rights reserved.
*
* This software is licensed under terms that can be found in the LICENSE file
* in the root directory of this software component.
* If no LICENSE file comes with this software, it is provided AS-IS.
*
******************************************************************************
@endverbatim
@par Example Description
How to configure and use, through the HAL LPTIM API, the LPTIM peripheral using LSE
as counter clock, to generate a PWM signal, in a low-power mode.
At the beginning of the main program the HAL_Init() function is called to reset
all the peripherals, initialize the Flash interface and the systick.
The SystemClock_Config() function is used to configure the system clock for STM32WB55RGVx Devices :
The CPU at 64 MHz
In this example, the LPTIM instance used is LPTIM1 and the low power mode is Stop mode.
The counter clock is LSE (32.768 KHz), Autoreload equal to 99 so the output
frequency (FrequencyOutput) will be equal to 327.680.
FrequencyOutput = Counter Clock Frequency / (Autoreload + 1)
= 32768 / 100
= 327.680 Hz
Pulse value equal to 49 and the duty cycle (DutyCycle) is computed as follow:
DutyCycle = 1 - ((PulseValue + 1)/ (Autoreload + 1))
DutyCycle = 50%
To minimize the power consumption, after starting generating the PWM signal,
the MCU enters in Stop mode. Note that GPIOs are configured in Low Speed to
enhance the consumption.
User push-button (SW1) pin (PC.04)is configured as input with external interrupt (External line 4),
falling edge. When User push-button (SW1) is pressed, wakeup event is generated and PWM signal
generation is stopped.
@note This example can not be used in DEBUG mode, this is due to the fact
that the Cortex-M4 core is no longer clocked during low power mode
so debugging features are disabled.
@note Care must be taken when using HAL_Delay(), this function provides accurate
delay (in milliseconds) based on variable incremented in SysTick ISR. This
implies that if HAL_Delay() is called from a peripheral ISR process, then
the SysTick interrupt must have higher priority (numerically lower)
than the peripheral interrupt. Otherwise the caller ISR process will be blocked.
To change the SysTick interrupt priority you have to use HAL_NVIC_SetPriority() function.
@note This example needs to ensure that the SysTick time base is always set to 1 millisecond
to have correct HAL operation.
@par Keywords
Timer, Low Power, PWM, Stop mode, Interrupt, LSE, Output, Duty Cycle
@par Directory contents
- LPTIM/LPTIM_PWM_LSE/Inc/stm32wbxx_hal_conf.h HAL configuration file
- LPTIM/LPTIM_PWM_LSE/Inc/stm32wbxx_it.h Interrupt handlers header file
- LPTIM/LPTIM_PWM_LSE/Inc/main.h Header for main.c module
- LPTIM/LPTIM_PWM_LSE/Src/stm32wbxx_it.c Interrupt handlers
- LPTIM/LPTIM_PWM_LSE/Src/main.c Main program
- LPTIM/LPTIM_PWM_LSE/Src/stm32wbxx_hal_msp.c HAL MSP module
- LPTIM/LPTIM_PWM_LSE/Src/system_stm32wbxx.c STM32WBxx system source file
@par Hardware and Software environment
- This example runs on STM32WB55xx devices.
- This example has been tested with STMicroelectronics P-NUCLEO-WB55
board and can be easily tailored to any other supported device
and development board.
- Connect PC1 (pin 30 in CN7 connector) to an oscilloscope to monitor the LPTIM1 output waveform.
- LSE oscillator must be mounted on the board, else this example does not work.
@par How to use it ?
In order to make the program work, you must do the following :
- Open your preferred toolchain
- Rebuild all files and load your image into target memory
- Run the example
* <h3><center>© COPYRIGHT STMicroelectronics</center></h3>
*/
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